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Reconstruction of past atmospheric aerosol load and composition (organic and inorganic): The case of the European aerosol since 1920 inferred from Alpine ice cores, and prospective for various polar ice cores.

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Seasonally resolved chemical ice core records available from the Col du Dôme glacier (4250 m elevation, French Alps), are useful in view to reconstruct past aerosol load of the free European troposphere from prior World War II to present. The extended array of inorganic (Na+, Ca2+, NH4 +, Cl-, NO3 , and SO42 -) and organic (carboxylates, HCHO , HUmic LIke Substances, dissolved organic carbon, water insoluble organic carbon, and black carbon) compounds and fractions already investigated permit to examine the overall aerosol composition and its change over the past. It is shown that the atmospheric load of submicron aerosols has been increased by a factor of 3 from the 1921-1951 to 1971-1988 years, mainly as a result of a large increase of sulfate (a factor of 5), ammonium and water-soluble organic aerosol (a factor of 3). It is shown that not only growing anthropogenic emissions of sulfur dioxide and ammonia have caused the enhancement of the atmospheric aerosol load but also biogenic emissions producing water soluble organic aerosol. This unexpected change of biospheric source of organic aerosol after 1950 needs to be considered and further investigated in scenarii dealing with climate forcing by atmospheric aerosol.
This finding on organic aerosol stimulates its study in Greenland and Antarctic snow and ice but dissolved organic carbon data often appear largely inconsistent and until now no critical review was conducted to understand the causes of these inconsistencies. A more consistent picture is here obtained by reviewing available data and, when needed, completing the data set with analyses of selected samples. These Antarctic and Greenland ice core data are briefly discussed with respect to natural (biomass burning, vegetation emissions) and anthropogenic sources (fossil fuel combustion) of atmospheric OC aerosol.